Television image pickup system



1941. T. w. SUKUMLYN TELEVISION IMAGE PICKUP SYSTEM 3 Sheets-Sheet 1 Filed Nov. 23, 1938 AWW Jyslm N VE N TOR 7710/1703, SIM/m4; BY 61440 Patented Nov. 11, 1941 rice Claims.

This invention relates to a system utilized in connection with television, and particularly for the transmission of signaling impulses corresponding to the illumination of elemental areas of an object being televised.

More particularly, the invention relates to a cathode ray tube device arranged to produce a signaling impulse through an input circuit of an amplifier, by virtue of the emission of secondary electrons, the emission being varied in accordance with the illumination of the elemental areas of an image.

Such cathode ray tubes are known. In these devices use is usually made of a mosaic of minute conducting elements mutually insulated from each other, upon which an electron image is focused. In some forms of these devices, the conducting elements may be photoactive. Under any circumstance, however, the mosaic is caused to emit secondary electrons, the emission at any elementary area being dependent upon the intensity of illumination of the corresponding part of the image. Accordingly, the potential at any point of the mosaic is dependent upon this emission, since the greater the rate of emission, the more positive is the area where it occurs. This variation in potential is utilized to afiect an input circuit by causing a variation in current flow in an impedance such as a resistance. The mosaic is appropriately scanned by a cathode ray gun in order to cause a discharge of current successively from the scanned elemental areas.

In devices of the prior art, the secondary emission from any elemental area is not entirely effective, for a majority of the secondarily emitted electrons return to the emitting surface without reaching the collecting anode. This is due to the fact that the electric field intensity in'the region between the mosaic and the collecting anode is low. Furthermore, upon being scanned by a cathode ray many of the electrons caused to be emitted by the action of the ray, return to the mosaic in the form of a continuous shower, and accordingly the mosaic is not discharged to the fullest degree possible in proportion to the charge on an elementary area upon which the scanning ray is incident. This effect further greatly reduces the signal strength. Another defect in tubes of the prior art is that the charge on an elemental area forms a charge on a relatively large capacity which is in parallel to the area. This large capacity lowers the applied potential for the input circuit. If the capacity were reduced to just that of the elementary area of the mosaic under the influence of the scanning ray, the consequent increase in the potential applied to the input of the amplifier would be several thousand times greater.

It is one of the objects of this invention to remedy these defects and thereby greatly to increase the signal strength.

This invention possesses many other advantages, and has other objects which may be made more easily apparent from a consideration of several embodiments of the invention. For this purpose there are shown a few forms in the drawings accompanying and forming part of the present specification. These-forms, which illustrate the general principles of the invention, will now be described in detail; but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of the invention is best defined by the appended claims.

Referring to the drawings:

Figure 1 is a diagram illustrating an embodiment of the invention;

Figs. 2 and 3 are fragmentary sectional views, greatly enlarged, of several forms of mosaic members which may be utilized in connection with the system illustrated in Fig. 1;

Figs. 4, 5 and 6 are diagrams similar to Figure 1 illustrating modified forms of the system; and

Fig. 7 is a view similar to Figs. 2 and 3 of another form of mosaic especially adapted to be utilized in the form of the invention illustrated in Fig. 6.

'In Figure 1 the evacuated cathode ray tube device I is shown as being made in any appropriate way, as for example from glass or other insulation materials.

In this form of the invention an electron image corresponding to the subject'which is to be televised, is cast upon a mosaic member 2. This member provides isolated minute conducting areas which are caused to have a potential corresponding to the intensity of the illumination of the image. For this purpose, an image is first focused as by lens system 3 (shown as exterior of the tube I) upon a photoactive cathode 4, having a photoelectric area on its left hand surface. This photoelectric cathode is made from a thin sheet of material arranged in such a way and is sufiiciently thin so that the illumination on its left hand surface causes emission of secondary electrons from the right hand surface, the intensity of the emission corresponding to the intensity of the illumination on the adjacent opposite surface. The electron beam thus produced is indicated in general by the lines 5.

In any appropriate manner, as for example by an electromagnetic coil 6 and a tubular anode I, the electron beam 5 is focused to produce the electron image upon the mosaic structure 2. The thin photo-cathode 4 is shown as connected to a negative terminal of any appropriate source of potential such as the battery 8, and the focusing anode I is shown as made suitably positive with respect to the cathode 4, as by being joined to an intermediate point of the battery 8.

The structure of the mosaic element 2 may take several forms. The important function is that the conducting elements of the mosaic be mutually insulated from each other, and that they be extended through the mosaic member 2 so that the potential existing on each conducting element is effective also on the right hand surface of the member 2.

In the form shown in Fig. 3, the mosaic member which may be very thin, forms essentially a sheet of small closely spaced but insulated conductors 9. This may be obtained by packing the openings II] in a perforated sheet I I of insulating material with any conducting substance.

Another way of constructing the two sided mosaic member is to mix metal particles in a binder of insulating material, such as porcelain powder in sodium silicate, and when the resulting mixture is dry, then to grind it in the form of a thin sheet, thus leaving many metal particles exposed on both sides of the sheet. Such a construction would be quite analogous to that illustrated in Fig. 3. a

In another method illustrated more particularly in Fig. 2, the two sided mosaic member is constructed by baking insulating enamel I2 over the wires I 3 of the fine mesh screen; then coating the screen so as to fill the apertures between the wires I3 with silver oxide in the form of a paste. This in turn may be heated in a reducing atmosphere to reduce the silver oxide to finely divided metallic silver. The baked filling I4 is indicated in Fig. 2.

It is possible to scan the right hand side of the mosaic 2 as by the aid of an electron gun structure I5 illustrated at the right hand portion of the figure. The impingement of the electrons on the elemental surface being scanned causes an intense and augmented stream of secondary electrons to be emitted from the elemental area. The electron gun structure is shown as having the usual elements such as a cathod I6 connected to the negative side of the battery 8, as well as a directing anode I! joined to an intermediate point of the battery 8, and the scanning elements I8. These scanning elements are so arranged, as is well understood, as to scan the right hand surface of the mosaic member 2 by the cathode ray I9. Assuming that the cathode ray electrons 29 emitted from the elementary area subject to the ray I9, have an intensity determined by the particular potential existing at that place. This in turn is determined by the electron charge on the particular area involved, as is determined by the electron image on the left hand surface of the member 2.

Due to the phenomenon of secondary electron emission, the intensity of the secondary emission is multiplied in a well understood manner. Advantage is taken of this in the present arrangement.

The loss of electrons from member 2 by emission of secondary electrons 29 from the right hand surface of member 2 may be replenished. In the present instance this is accomplished by I9 is of constant intensity, the secondary the aid of a second electron gun structure 22 located in the branch 2I of the tube I. This electron gun structure also includes the well known elements such as the cathode 22, directing anodes 23 and 24 and the scanning elements 25. The cathode ray 26 is thereby arranged to scan the left hand side of the member 2 and to cause electrons to be passed to the mosaic member 2.

The complete circuit for the replenishment of the electrons may be traced from the negative side of the battery 8, the cathode 22, the mosaic member 2, a collecting anode 2'! which is in the form of a cylinder adjacent the left hand side of the member 2, back to the positive side of the battery 8. The rate at which the mosaic member 2 is scanned by the ray 26 may be the same or different from the rate of scanning by the oathode ray I9. The electron ray 28 can be so arranged as to provide a copious source of electrons. By ensuring that the relative potential differences between the cathode 4 and the collecting anode 21 be rather low, the electrons 28 secondarily emitted to the anode 2'! are relatively few.

On the other hand, the electrons 29 secondarily emitted from the right hand side of the member 2 due to the impact of electrons in the ray I9, are quite copious. These electrons 29 are shown as collected on a collecting anode 30 of comparatively small capacity. The path of the current includes a resistance 3| connected to the positive side of the battery 8, through the battery, and thence to the cathode I 6 of gun structure I5. Due to the fact that the capacity of the anode 30 is small, a considerable potential difference is impressed upon the resistance 3|. Accordingly the input circuit to the amplifier system 32 has impressed upon it a comparatively large variation in potential difference for each signalling impulse created by the flow of secondary electrons to the collecting anode 30. Due to the large volume of low velocity electrons in the cathode ray 26, the mosaic screen member 2 is maintained at a relatively low potential in spite of a considerable secondary emission. Therefore there is a comparatively high electric field strength between the mosaic member 2 and the anode 30 which ensures that substantially complete collection of all secondary electrons can be obtained, comparatively few of the stream 29 being returned to the member 2.

The input circuit for amplifier system 32 is bridged across the upper terminal of the resistance 3| and the negative terminal of battery 8.

In the usual type of electron image pickup device, the minute elements of the mosaic member are in capacitive relation to a large common plate serving as a support for these elements. The capacity thus formed parallels the input of the amplifier system. In such a pickup the electrostatic capacity is of the order of five hundred times as great as obtained when a collecting anode such as anode 30 is utilized. Accordingly there is a consequent gain by the aid of this invention in pickup sensitivity of some hundreds of times on this account alone.

It is possible to eliminate the electron gun scanner 20 utilized for replenishing the electrons on the mosaic element 2, by permitting a leakage of current between the support for the elements of the mosaic to these elements. Such an arrangement is shown in Fig. 4.

In this case the electron gun I5 operates as before upon the right hand side of a mosaic member 33. The electron image is produced upon the mosaic member 33 in the same way as before;

that is, by the aid of the thin photoactive cathode 4, and is focused upon the member 33 as by the anode l and electromagnetic coil 6.

In this case, however, the insulation support for the finely divided metallic elements of member 33 is connected by lead 34 to a positive point of the battery 8. If this insulation support is of the character described in connection with Fig. 2, the ceramic matrix may be suitably arranged to permit a slight leakage of current through the matrix to the isolated elements of the mosaic 33. The collecting anode 35, as before, serves to pass current through the resistance 36 operating to affect the input circuit of the amplifier system 31.

Another permissible simplification is illustrated by the system shown in Fig. 5. In this case the photoactive cathode 4 is omitted. Instead, the mosaic member 38 is so arranged that the exposed area of the conducting elements are photoactive on that side which faces the lens system 3. Accordingly there is a direct electron image produced upon the mosaic member 38. In other respects the system is identical with that illustrated in Fig. 1. As before, the collecting anode 39 is arranged to pass current through the resistance 40 across which a correspondingly high potential difference exists. This high potential difference is utilized for the input circuit of the amplifier system 37.

A somewhat similar system is illustrated in Fig. 6'. In this case, however, the scanning electron gun operating on the right hand surface of mosaic member 4| is omitted. This is rendered possible by the use of a specific type of mosaic member which will now be described.

There is a photoactive cathode 42 operating as before to emit a beam of secondary electrons 43 so as to produce an electron image on the left hand surface of the mosaic member 4!. The beam 43 is focused properly by the usual provisions of a series of anode plates 44, 45, 46 and 41 respectively at higher and higher potentials as they progress from the photocathode 42.

A small portion of the member 4| is shown 1n greatly exaggerated size in Fig. '7. There it is seen that there is a thin metal foil 55 which is oxidized to form an oxide layer 56. Deposited by evaporation are minute metallic particles 51 forming the mosaic. However, these metallic particles may be omitted for certain conditions of velocity of cathode rays.

Now assuming that there is an electron image. on the left hand surface of member 4|, the the scanning ray 48 of the electron gun 20 causes the emission of secondary electrons through the,

oxide layer 56 and the thin metal foil 55. This secondary emission occurs from the area which is being scanned by the ray 48. The electrons in the secondary emission beam 49 are collected by an anode 50 of small capacity. The anode 50 is connected to the positive terminal of the battery 8.

In order to converge the secondary emitted electrons toward the plate 50, use may be made of a conventional directing anod'e .As before, the current set up through the anode 50 is utilized to produce a high potential difference across a resistance 52, across which the innput circuit of the amplifier system 53 is connected.

In this case the thickness of the elements making up the structure 4! must be such as to fulfill several requirements. Thus it must be thick enough to prevent secondary emission due to the photoelectron beam 43, and it must also provide a leakage path of proper resistance to allow the elementary area of the mosaic to be discharged in something close to a frame period, that is to a complete scanning by the rays 48. It must be thin enough, however, to permit copious emission of secondary electrons due to the impingement of the scanning ray 48. The connection 54 to the member 4| is made to the metal foil member 55.

Due to the use of a small capacity of the collecting anode 50 and to the use of secondary emitted electrons in the stream 49, a high degree of multiplication is effected.

What is claimed is:

1. In a system of the character described, means forming a mosaic of small elements of electrically conducting material and capable of secondary emission of electrons, means for forming a charge image on the mosaic, a cathode ray means for scanning successive elemental areas of said mosaic to produce secondary electron emission, a collecting anode spaced from the mosaic and having a potential suificiently high with respect to the mosaic to collect most of the secondarily emitted electrons, an output circuit associated with said anode in which said electrons are active, a second cathode ray means for electrons operating over the surface of the mosaic opposite from the scanning means, and a second anode spaced from the mosaic and maintained at a sufficiently high potential with respect to the mosaic for collecting most of the electrons emitted from said opposite surface.

2. In a system of the character described, means forming a mosaic of small elements of electrically conducting material and capable of secondary emission of electrons, means for forming a charge image on the mosaic, a cathode ray scanning means for successive elemental areas of said mosaic to produce secondary electron emission, a collecting anode spaced from the mosaic and having a potential sufficiently high with respect to the mosaic to collect most of the secondarily emitted electrons, an output circuit associated with said anode in which said electrons are active, and a second cathode ray gun scanning the surface of the mosaic opposite the cathode ray scanning means for passing electrons to said mosaic.

3. In a system of the character described, a photoactive cathode upon which an image may be projected, said cathode having an emergent side for secondary electrons, means forming a mosaic of small elements of electrical conducting material having a surface exposed to said secondary electrons, and upon which a charge image is formed, said mosaic having an opposite surface, a cathode ray means for scanning successive elemental areas of said opposite surface to produce secondary electron emission, a collecting anode spaced from the mosaic having a potential sufficiently high with respect to the mosaic to collect most of the secondarily emitted electrons, an output circuit associated with said anode in which said-electrons are active, a second cathode ray means for replenishing electrons on the image surface, and an anode for collecting secondary electrons from said image surface.

4. In a system of the character described, means forming a mosaic of small elements of photoelectrically active conducting material capable of secondary emission, said elements having areas exposed on both sides of the mosaic, means forming an illuminated image on one side of the mosaic, a cathode ray means for scanning successive elemental areas on the other side of the mosaic to produce secondary electron emission therefrom, a second cathode ray means operating over the image surface of the mosaic to replenish saic, a pair of cathode ray means for respectively scanning successive elemental areas on opposite sides of the mosaic, a pair of anodes spaced from the mosaic and on opposite sides respectively thereof, one of said cathode ray means serving to produce secondary emission from the mosaic, an output circuit in which said electrons are active, the other cathode ray means serving to replace the electrons on the mosaic, said anodes being maintained at a suitable potential above the mosaic to capture respectively most of the secondary electrons emitted in response to said rays, the anode which captures the electrons emitted due to the replenishing ray being at a higher potential than the other anode, the other anode being connected to the output circuit.

' THOMAS W. SUKUMLYN. 

